Waterproof membranes without the protection of a green roof need to be replaced every 10 to 20 years while some green roofs in Europe are over 100 years old and still waterproof (Earth Pledge, 2005). This effectively helps reduce landfills by reducing the amount of membranes being thrown away.

In the 1880s, German roofer H. Koch put a layer of soil and gravel on tar roofs to prevent roof fires. These roofs were germinated by wild seeds, and the modern green roof was inspired 70 years later when these roofs were found to be still intact and waterproof, having survived 2 world wars (Earth Pledge, 2005).

A green roof has a burning heat load of 3 kWh/m² while a 3-ply bitumen roofing system, a common membrane type, has a burning heat load of 50 kWh/m². (M Koehler, 2003) This means that the heat from a fire on a green roof will be 1/16th the heat from a bitumen system.

Some plants are more fire resistant then others. Succulents such as sedums contain water and are difficult to burn. Grass, however, can dry out during drought conditions and become more flammable.

Studies have shown that patients recover more quickly when they have access to green spaces.
Hospitals with open green spaces record patient check-out times 2.5 days earlier then hospitals without green spaces (Peck, 2008).
The 10,000 sq ft green roof on the Schwab Rehabilitation Hospital in Chicago also serves as a rooftop park and garden for horticultural therapy, a process in which plants and gardening activities are employed to improve body, spirit and mind (Green Roofs for Healthy Cities, 2005).

A 1988 study demonstrated that the availability of a natural view can be instrumental in the alleviation of daily stress, physical ailments, a decrease in the number of sick days taken, and an increase in worker satisfaction and productivity (Kaplan, 2001).

According to the US Green Building Council, green roofs can receive up to 23 LEED credits for various categories including sustainable sites, water efficiency, energy and atmosphere, and innovation and design process.

Environmental

Green roofs reduce and delay stormwater runoff, helping to mitigate combine sewage overflows (CSOs), which result when storm water floods a city's sewer system and discharges raw sewage into the local watershed. Green roofs also filter pollutants from rainwater, roofing materials, and atmospheric deposition.

Case Studies:
• Extensive green roofs can retain an average of 75% annual rainfall and delay runoff by 3 to 4 hours (Susan K. Weiler, 2009).
• A study conducted by Environment Canada found that if Toronto covered 6% of available roof space with green roofs, it could retain 127 million cubic feet of rain water per year. The storage tank needed to hold the same amount of rainwater would cost $60 million while the green roofs needed would cost $45 million.
• The 10.4 acre green roof on the Ford Dearborn Truck Plant retains approximately 4 million gallons of rainwater each year (XeroFlor).
• The 18,000 square foot green roof atop Radio City Music Hall will prevent approximately 566,000 gallons of water from entering New York City's sewage system (environmentalleader.com).

Air temperatures in urban areas have increased by 2ºF per decade over the last 50 years and are now 7 to 11ºF higher than in the surrounding undeveloped areas. Green roofs can alleviate the Urban Heat Island effect by covering black rooftops, one of the hottest factors in the urban environment, with cool, green surfaces.

Green roofs absorb airborne particles and carbon dioxide while releasing oxygen, effectively filtering and cleaning our atmosphere. By reducing the ambient summer temperature around a building, less energy is needed for air conditioning, and thus produce fewer CO2 emissions.

Case Study:
• The green roof on the Ford Truck Plant in Dearborn Michigan is predicted to improve the air quality around the building by 40% by absorbing dust and breaking down hydrocarbons (Earth Pledge, 2005).